1. Field of the Invention
The present invention relates to a pressure measuring apparatus based on magnetostriction, and more particularly, to an apparatus in which a coil is constructed outside a vessel whose pressure will be measured, and ultrasonic waves necessary for pressure measurement are directly generated and measured inside the vessel using a magnetostrictive ultrasonic transducer having a vibration unit placed inside the vessel, so that an internal pressure of the vessel can be measured even in a low vacuum or high vacuum and under high atmospheric pressure or higher. Furthermore, the present invention relates to an apparatus that can transmit ultrasonic waves necessary for pressure measurement without damage or modification of a vessel.
2. Background of the Related Art
In general, in various manufacturing process such as the semiconductor and LCD fabrication, the measurement of the internal pressure of a vessel plays an important role in parameter control in process. When it is sought to measure the degree of vacuum, that is, the pressure of a vessel, a capacitance diaphragm gauge (CDG) is generally used.
Such a capacitance diaphragm gauge is configured such that it is mounted inside a vessel whose pressure will be measured and measures the pressure of the vessel. However, this method using the capacitance diaphragm gauge is complicated in that, before the degree of vacuum or pressure inside the vessel is measured using the capacitance diaphragm gauge, the degree of leakage of vacuum must be checked and, after the capacitance diaphragm gauge is constructed, the inside of the vessel must be made vacuum-tight. Furthermore, the capacitance diaphragm gauge has a limitation in that it can be used only in a low vacuum state.
A pressure measuring apparatus, which generates and receives ultrasonic waves outside the vessel by solving the problems, has a merit in that it is not required to check the degree of leakage of the vessel. However, a vessel is generally made of metal material, such as stainless steel, so as to withstand a difference between an internal pressure and an external pressure. Thus, when it is desired to transmit ultrasonic waves from the outside of the vessel to the inside thereof in order to measure the pressure inside the vessel, there is a disadvantage in that the ultrasonic waves are hardly transmitted to gas inside the vessel due to a great difference in acoustic impedance between the material of the vessel and the internal gas. Similarly, there is also the same problem in that the ultrasonic waves are rarely transmitted from the inside to the ultrasound measurement device at the outside of the vessel. Therefore, there are problems in that it is difficult to transmit ultrasonic waves as described above and pressure measurement is difficult since the transmitting efficiency of ultrasonic waves between the outside and the inside of the vessel is very low. Therefore, there is a need for an apparatus which can efficiently transmit ultrasonic waves so as to measure pressure inside a vessel using the ultrasonic waves.